Binocular indirect microscopes (BIOM) are known that allow a doctor to observe the interior of the patient's eye and in particular the fundus of the patient's eye. A BIOM typically includes a binocular prism set with an integral illumination system forming a unit that is worn on the doctor's head, the illumination system including a light bulb and a mirror to direct the light. The BIOM also includes a hand held condensing lens or indirect lens of the type manufactured by Volk, Inc. In use, the doctor positions the binocular prism/illumination system on his head so that he can look through the prisms. The doctor holds the condensing lens in close proximity to the patient's eye to be examined. The doctor then adjusts both the position of the condensing lens and his position so that he can look into the patient's eye through the hand held lens and through the head mounted binocular prisms with the interior of the eye being illuminated by the head mounted illumination system. The BIOM generates a real image of the patient's fundus that is observed by the doctor via the prisms and condensing lens.
Although the BIOM was invented in 1911 by Gullstrand, it is still used today with little change, the improvements over the earlier systems resulting from better optical manufacturing techniques and the use of anti-reflection coatings. Both the early and modern BIOMs share the same problems. In particular, for a BIOM examination, the patient's pupil must be dilated with mydriatic drugs in order for the doctor to view the patient's fundus. As a result, the patient's pupils are unable to respond to varying light levels for several hours; the patient is dazzled by bright lights; under dark conditions the patient has difficulty seeing; and the patient's ability to read is dramatically hampered. BIOMs are also difficult to use because the image produced by the condensing lens is indirect and therefore upside down with left and right reversed. Further, there is an increased possibility of misdiagnosis with a BIOM since the clinician must interpret the upside down/left-right reversed image relative to the patient's real orientation. Also, since the patient's eye, hand held condensing lens, head mounted prisms and the doctors eyes must be aligned coaxially to perform an examination, the physician must typically undergo various positioning maneuvers before the necessary alignment is obtained to conduct the examination.